Some databases store data in columnar data tables for improved compression of stored data. For example, some approaches to in-memory database architectures rely upon column stores. To optimally compress new data written to columnar data tables, a database management system associated with such a database typically executes a merge process to merge newer data, which are typically temporarily stored in a delta part of a table with previously stored data, which are retained in a main part of the table. Such a merge process can require a significant amount of time due to reorganization of the columnar table that typically during the merge process. Because access to the data of the columnar data tables is restricted during a merge process, responsiveness to queries or other access requests, such as for example those formed using a data manipulation language (DML), a data query language (DQL), or the like can be delayed, sometimes for an extended period of time depending on the size of the delta part and main parts being merged.